1. Field of the Invention
The present invention relates to a semiconductor integrated circuit having a plurality of functional blocks and, more particularly, to a semiconductor integrated circuit comprising a semiconductor device having a tunnel junction which has small capacitance and in which single-electron tunnel effect takes place.
2. Description of the Related Art
Semiconductor integrated circuits such as memories and logic circuits, each comprising MISFETs, are known. Their advancement has been attained by making MISFETs smaller and smaller.
An integrated circuit of this type consumes 1 femtojoule to perform one logic operation. In actual operation, however, it spends as much as 10 femtojoules for one logic operation, because some load is applied to it. Each device incorporated in the circuit consumes 10 microwatts when the clock frequency used is 1 GHz. If the circuit has 100 million logic gates, it will probably consume as much as 1 kilowatt.
MISFETs have been miniaturized to enhance the integration density and operating speed of integrated circuits. It is now difficult to miniaturize MISFETs further for reasons of various problems such as a higher possibility of punch-through and a leakage current through a thin gate electrode.
Furthermore, the operating speed can hardly be increased even if the MISFETs are made much smaller, due to the increased peripheral capacitance of the integrated circuit. Since, each MISFET is now so tiny that only hundreds of electrons are moving to activate the MISFET, even if only one electron is trapped in the gate oxide film, the drain current will change very much, about several tens of percent. Due to this change in the drain current, the MISFET will possibly make errors while operating.
In the course of miniaturization of the device, new phenomena are observed. Novel devices in which new phenomena are positively used have been developed. Among them is a single-electron transistor, or a SET (see IEEE Trans. Magnetics, Vol. MAG-23, pp. 1142-1145). The SET utilizes a phenomenon called "coulomb blockade" which occurs in small tunnel junctions. As shown in FIG. 1, the SET has two tunnel junctions 1 and 2. Current flowing through the tunnel junctions is controlled by a gate capacitive-coupled to an electrode located between the junctions 1 and 2.
It is proposed that the SET be incorporated in the circuit shown in FIG. 28. However, what measures should be taken to enable the SET to detect information has not yet been known.
A voltage controlling SET system is about e/C, where C is the capacitance of the small junctions. Obviously, this voltage is far lower than the power-supply voltage of 3V applied to drive MOS transistors commonly used at present. The current flowing in the SET is 1 nA or less, far less than the current flowing in a MOS transistor. If SETs are incorporated in an LSI together with other types of active devices, such as MOS transistors, there will arise great problems because of the difference between each SET and each other device in terms of control voltage and control current.
The higher the integration density of an integrated circuit, the greater the power consumption of the circuit. How much the integration density can be increased depends, after all, on whether or not heat-related problems can be solved. Even if the heat-related problems are solved, there are other problems hindering further advancement of integrated circuits, such as the limit to the miniaturization of MOSFETs and the limit to the advantage resulting from the miniaturization of MOSFETs.
As mentioned above, no methods have yet to be developed to enable an SET to detect information. The voltage controlling SETs is about e/C. (C is the capacitance of the small junctions which the SET has.) This voltage is order of 1 mV, i.e., the lowest voltage needed for driving the smallest possible device that can be provided by the manufacturing techniques which are available at present.
As indicated above, the power-supply voltage applied to drive MOS transistors commonly used at present is 3V. This voltage will be reduced to 1V when MOS transistors are made smaller to have a 0.1 micron size. As already pointed out, the current flowing in the SET is 1 nA or less, much less than the current that flows in a MOS transistor.